There has been known a heat exchanger which allows a refrigerant and air to exchange heat and includes a plurality of vertically arranged flat tubes, fins joined to the flat tubes, and two header collection pipes, each of which is connected to an associated one of the ends of each of the flat tubes (see, e.g., Patent Document 1).
A heat exchanger disclosed by Patent Document 1 is divided into two vertically arranged heat exchange regions. Each of the two heat exchange regions is further divided into three vertically arranged heat exchange sections. The two heat exchange regions are connected in series when the heat exchanger functions as an evaporator, and a refrigerant flows from each of auxiliary heat exchange sections of a lower auxiliary heat exchange region to an associated one of principal heat exchange sections of an upper principal heat exchange region.
In each of the two header collection pipes, communicating spaces each communicating with the plurality of flat tubes are formed in a one-to-one relationship with the heat exchange sections. In the heat exchanger described above, a refrigerant that flowed into each of the communicating spaces is distributed into the plurality of vertically arranged flat tubes communicating with an associated one of the communicating spaces, and exchanges heat with the air while flowing through the flat tubes.